Prior art vehicular exhaust mufflers typically comprise an array of parallel tubes supported by transversely extending baffles and mounted within a generally tubular outer shell of circular or oval cross section. The array of tubes in the prior art muffler typically comprises an inlet tube connectable to the exhaust pipe coming from the engine, an outlet tube connectable to the tail pipe and one or more additional tubes to provide communication between the inlet and outlet. The baffles of the prior art muffler typically conform to the cross-sectional shape of the outer shell such that the baffles and the outer shell define a plurality of chambers within the muffler. The pipes disposed in the prior art muffler communicate with one or more of the chambers. For example, certain pipes extending through a chamber might be perforated or louvered to allow the exhaust gases to expand into the chamber and/or to permit a controlled amount of cross flow between two perforated tubes in the expansion chamber. The prior art muffler could also include a tuning tube extending into an at least partly enclosed low frequency resonating chamber for the purpose of attenuating a fairly narrow range of low frequency noise.
The noise and pressure characteristics of exhaust gases vary widely from one engine type to another. Thus, exhaust mufflers are carefully engineered for each vehicle engine type to ensure that the muffler attenuates noise properly for its intended vehicle and achieves the specified levels of noise and back pressure. The parameters that affect these performance characteristics include the cross-sectional area of the tubes within the muffler, the cross-sectional area encompassed by perforations or louvers, the length and cross-sectional dimensions of tuning tubes, the volume of the various low frequency resonating chambers and expansion chambers and so forth.
In addition to the acoustical design parameters, automotive engineers must contend with the limited available space on the vehicle. In particular, other structures on the vehicle such as the gas tank, the passenger compartments, the trunk and spare tire well, the drive train and suspension components typically have set volume and location requirements that limit the number, the size and the shape of the locations available for the muffler. Additionally, most automobile manufacturers establish sight lines and ramp clearances above which all structural components, including the exhaust system, must be disposed. These various space limitations and controls have imposed servere design constraints and limitations on the manufacturer of the prior art mufflers. In particular, the muffler manufacturer could alter the length of the prior art muffler to fit the available space and could select an appropriate size oval or circular cross section in an attempt to match the space envelope on the vehicle. However, in virtually all situations, the manufacturer of the prior art muffler was limited to generally rectangular top, bottom and side plan view configurations of the muffler and a circular or oval transverse cross section. As a general rule, it becomes increasingly more difficult to achieve specified noise and back pressure levels as the volume or size of the muffler is decreased. Smaller mufflers tend to increase back pressure and limit the number of acoustical tuning options that are available.
The prior art includes various stamp formed mufflers. Many of these prior art stamp formed mufflers have comprised a pair of stamp formed plates secured in juxtaposed relationship, with the stamp forming defining a circuitous route for the exhaust gases to follow. The particular circuitous route of these prior art stamp formed mufflers was intended to attenuate the exhaust gas noise. Examples of such prior art mufflers include U.S. Pat. No. 2,484,827 which issued to Harley on Oct. 18, 1949 and U.S. Pat. No. 3,638,756 which issued to Thiele on Feb. 1, 1972. Other prior art stamp formed mufflers have included at least one pair of stamped internal plates which define tubes and/or baffles and a pair of stamped external shells to define an enclosure around the internal plates. Prior art mufflers of this general construction are shown in: U.S. Pat. No. 4,132,286 which issued to Hasui et al on Jan. 2, 1979; U.S. Pat. No. 4,456,091 which issued to Blanchot on Jun. 26, 1984; and British Pat. No. 632,013 which issued in 1949. Other prior art mufflers have included stamp formed external shells with internal components comprising both tubular and stamp formed components, such as the muffler shown in Japanese Pat. No. 59-43456, while still others have included stamp formed internal components with conventional wrapped outer shells, such as the muffler shown in U.S. Pat. No. 4,396,090 which issued to Wolfhugel on Aug. 2, 1983.
Recently there have been several significant engineering improvements in mufflers fabricated from a plurality of formed sheets of metal. In particular, the metal sheets of these mufflers are appropriately deformed by available processes such as stamp forming, hydroforming, explosion forming or magnetic forming. For example, a formed muffler with an array of tubes including a tuning tube and with a low frequency resonating chamber and expansion chambers is shown in U.S. Pat. No. 4,700,806 which issued to Jon Harwood on Oct. 20, 1987 and which is assigned to the assignee of the subject invention. The mufflers shown and described in U.S. Pat. No. 4,700,806 afford many engineering and manufacturing advantages in view of their stamp formed construction, while also achieving sound attenuation options that had not previously been available with stamp formed mufflers. The disclosure of U.S. Pat. No. 4,700,806 is incorporated herein by reference.
As noted above, the prior art conventional muffler formed with tubular internal components, baffles and a wrapped outer shell is typically of generally rectangular configuration in its top, bottom and side plan views and oval or circular in transverse cross-section. Also as noted above, this limitation on the shape of the muffler has created significant challenges to the automotive engineers attempting to design the exhaust system within the limited space envelopes on the vehicle. The above described prior art stamp formed mufflers have also generally conformed to this rectangular plan view configuration to define a generally convex polyhedral external shape. However, certain of these prior art stamp formed mufflers have somewhat softened the polyhedral configuration with tapers at the opposed ends, such as in the above referenced U.S. Pat. No. 3,638,756 and U.S. Pat. No. 4,132,286. U.S. Pat. No. 4,700,806 also shows that the rectangular side elevational view can be altered with a tapered end wall.
Further advancements in muffler construction are shown in co-pending patent application Ser. No. 061,876 which was filed by Jon Harwood et al on Jun. 11, 1987 and is now U.S. Pat. No. 4,760,896 which is directed to an exhaust muffler with angularly aligned inlets and outlets. In particular, co-pending application Ser. No. 061,876 shows a generally polyhedral exhaust muffler of generally pentagonal top plan view configuration achieved by truncating one corner of an otherwise rectangular top plan view to enable the muffler to be placed in proximity to the differential of a rear wheel drive vehicle. Co-pending application Ser. No. 061,876 further shows that the stamp formed construction enables the inlets and outlets of the muffler to be angularly aligned relative to one another and relative to the centerline of the muffler, and further enables at least one inlet or outlet to extend from the top or bottom of the muffler, thereby obviating the need for long tubular bends and enabling the muffler to be placed in closer proximity to other structures on the vehicle. A similar disposition of a muffler inlet and/or outlet is shown in co-pending application Ser. No. 061,913 which also was filed by Jon Harwood on Jun. 11, 1987 and is now U.S. Pat. No. 4,759,423 which is directed to the tube and chamber construction for an exhaust muffler. These co-pending applications are assigned to the assignee of the subject invention and their disclosures are incorporated herein by reference.
Several of the above identified prior art references show stamp formed mufflers where the external shells include indentations to achieve or contribute to a particular required circuitous flow of exhaust gases. For example, the above described U.S. Pat. No. 4,700,806 and the co-pending applications all show formed mufflers wherein the external shells include creases or indentations which extend into contact with the internal plates to define chambers surrounding the array of tubes in the muffler.
Despite the significant recent advances in stamp formed mufflers, the mufflers have defined an exterior profile or space envelope, relative to other parts of the vehicle, of generally convex polyhedral shape. It is now realized that this geometric limitation may create difficulties in attempting to position an acoustically acceptable muffler within the limited space on a vehicle.
In view of the above, it is an object of the subject invention to provide a muffler comprising a plurality of stamp formed components configured to conform closely to the shape of other structures on the vehicle.
It is another object of the subject invention to provide a muffler having a plurality of stamp formed external shells, at least one of which is stamped to conform to the available space on a vehicle.
An additional object of the subject invention is to provide a muffler having at least one stamped external shell which is generally concave in configuration and conformal with respect to at least one other structural component on a vehicle.
A further object of the subject invention is to provide a vehicular exhaust muffler having a plurality of external shells, at least one of which is concave to substantially follow an interference zone surrounding at least one other structural component on a vehicle.
Still a further object of the subject invention is to provide an exhaust muffler having at least one external shell configured to at least partly surround another structure on the vehicle.